1. Field of the Invention
This invention relates to wireless communication systems, and more specifically to a method of adaptively allocating resources at a base station to maximize the wireless communication device standby time in a system using a quick paging channel.
2. Description of the Related Art
FIG. 1 is a block diagram showing a typical modern wireless communication system 10. The system is comprised of several remote stations 12 and a series of base stations 14 (only one is shown). Mobile stations 12, such as personal wireless communication handsets, communicate with the base stations 14 over forward link channels 18 and reverse link channels 20. Forward link channels 18 are structured to consist of traffic channels and overhead channels, including one or more paging channels. A paging channel 22 is used to communicate from the base station 14 to the mobile station 12 when the mobile station 12 is not assigned to a dedicated channel.
Code Division Multiple Access (CDMA) 2000 is a well known standard used in wireless communication systems. In CDMA2000, a quick paging channel (QPCH) 24 contains two-identical-bit messages that direct the mobile stations 12 to monitor their assigned slot on the paging channel 22. Use of the QPCH 24 allows considerable improvements in standby time. In this circumstance, the mobile station 12 only needs to decode the two-identical-bit messages on the QPCH to determine if it needs to receive an incoming page. The QPCH 24 is a new feature in CDMA2000.
The QPCH reduces the amount of time a mobile station is awake. As used herein, a mobile station is awake when it is consuming power from a power source to demodulate a channel using a radio frequency receiver and demodulation hardware. As used herein, the term xe2x80x9cwake upxe2x80x9d is used to mean activation of, and application of a power source to, hardware necessary for demodulating a paging signal. Similarly the terms xe2x80x9csleepxe2x80x9d and xe2x80x9cgo to sleepxe2x80x9d refer to the deactivation of the hardware for the purpose of conserving a power source in the mobile station.
No error correction coding or interleaving is used for the QPCH paging indicator bits. Consequently, the time awake to receive the bits is small compared to the time awake to receive the regular paging channel slot. A pair of QPCH paging indicator bits indicate to the mobile station whether it is to wake up for its paging channel slot to receive a page. On-off keying is used by the base station to transmit the QPCH bits. For example, for one value the base station transmits a spread spectrum signal at a given power level during the bit time period using a particular spreading code and for the other value the base station does not transmit any power during the bit time period using the particular spreading code.
The paging channel 22 and the QPCH 24 are divided into slots. For example, the QPCH is divided into 80 ms slots called QPCH slots. The beginning of a QPCH slot occurs 100 ms earlier in time than the beginning of the associated PCH slot. Each QPCH slot is divided into four 20 ms frames. In a QPCH slot, a mobile station""s first paging indicator bit will be in one of the first two 20 ms frames of the QPCH slot. A mobile station""s second paging indicator bit will occur in the frame two frames after the frame containing the mobile station""s first paging indicator bit. If the mobile station receives two paging indicator bits in a slot commanding the mobile station to wake up, the mobile station will wake up and monitor the paging channel 22.
In conventional IS-95A/B systems, the standby time of the mobile station 12 is independent of the channel condition or the power allocation at the base station 14. On the other hand, the base station 14 can adjust various parameters of the QPCH 24 that have an affect on the ability of the mobile station 12 to demodulate the QPCH 24. For example, the transmission power 26 of the QPCH 24 can be adjusted at the base station 14. CDMA2000 specifies that the QPCH""s transmission power 26 relative to the pilot power range from 2 dB to xe2x88x925 dB.
Also, the number of quick paging channels transmitted by the base station 14 also can be adjusted at the base station 14. CDMA2000 specifies that one to three quick paging channels 24 can be allocated to each supported CDMA channel. The number of quick paging channels 30 influences the probability of a collision occurring. Collisions occur if the QPCH""s indicator positions for two mobile stations 12 happen to be the same. In this case, if one of the mobile stations has a page, the base station 14 will send a signal to wake the mobile station 12. Because two mobile stations have the same QPCH indicator positions, both mobile stations 12 will wake up. Additionally, the data rate 28 of the QPCH 24 can be adjusted at the base station 14. CDMA 2000 specifies that the data rate 28 be 4800 bps or 9600 bps. With a higher data rate 28, the base station can transmit more information, therefore there are more QPCH paging indicator positions.
However, there are trade-offs in adjusting the above parameters. Although using a higher data rate 28 reduces the chance of collision, it is well known that using a higher data rate with transmission power remaining the same results in worse performance in demodulation of the QPCH. This can cause an increased number of false page indications, thereby increasing the number of times the mobile station 12 is caused to wake up unnecessarily.
Additionally, one concern with respect to the base station 14 is the available power and transmission capacity of the base station. If more resources are allocated to the QPCH, there will be fewer resources allocated to the forward link traffic channel, which may result in the reduction of total system capacity. When the network load is high, i.e., when there are many active users or a high data rate request, it is likely that the service provider will prefer to provide service to the active users rather than increasing the standby time of the idle users. On the other hand, if the network load is low, the service provider has the ability to allocate more resources to the QPCH 24 while maintaining adequate services for the active users.
What is needed is a method of adaptively adjusting parameters of the QPCH 24 at the base station 14 according to current available network resources to maximize the standby time of the mobile stations 12.
The invention satisfies the aforementioned needs by providing a method of adaptively allocating network resources to improve performance of a wireless communication device in a system in which a base station transmits a QPCH signal. The method includes identifying at least one parameter of the QPCH signal at the base station, monitoring the network load at the base station; and adaptively adjusting the at least one parameter at the base station based on the network load, such as the QPCH transmission power, to influence the performance of the wireless communication device.